Induction electric furnace



March 20, 1934. NORTHRUP 1,951,881

INDUCTION ELECTRIC FURNACE Filed July 17, 1929 Patented Mar. 20, 1934 PATENT" oFFica mnuo'rron anaemic summon Edwin Fitch Northrup, Princeton, N. J... assignor to Ajax Electrothermic Corporation, Ajax Park, N. J., a corporation of New Jersey Application July 1'1, 1929, Serial No. 378,835 comma. (ci ia-43.1)

My invention relates to induction electric furnaces for the melting and/or for the treatment while melted of fusible materials.

A main purpose of my invention is to save furnace time in treating furnace contents in which air and gases must .be allowed to rise to the surface.

A further purpose is to increase the pressures plan view of a structure capable of carrying outmy invention.

In the drawing similar numerals indicate like parts.

In the manufacture of glass of the better quality such as Pyrex glass and optical glass, for example, it is extremely desirable to remove air from the body of the glass as fully as possible. For this purpose in the present practice the glass is kept molten for a long time in order to allow the air to come to the surface. This requires an excessive amount of furnace time for this operation. With some metals and with other materials, metallic or non-metallic, it is quite desirable to eliminate air or gases or vapors as much as possible and as quickly as possible. In other words, glass represents an excellent illustration, but not the only one, of the desirability of getting rid of the air or other gas or vapor which may be present within a molten mass.

From the standpoint of increasing the density it is also desirable in many lines to increase the pressure upon and within the molten; metal. Without altering the position of a molten charge within a furnace my invention provides not only a very excellent method of eliminating air, gas or vapor but for increasing the pressure upon a molten mass, which increase is distributed throughout the mass and is secured by cooperation of all of the elements of the mass.

' My invention is effected by centrifuging the molten material preferably while the full temperature is maintained.

In the drawing I show a centrifuging mechanism which is intended to be diagrammatic in large measure. The apparatus includes supports for two furnaces and connections for the heating and melting of furnace charges and for the maintenance of electric current connections with the furnace during the time of centrifuge operation.

Figure l is a side elevation and Figure 2 is a top plan view of structure by which my invention may be carried out.

Figure la is a fragmentary view allied to Figure 1.

Upon pedestal 5 is mounted a revoluble head 6 carrying a gear 7 by which the head may be r0- tated upon suitable bearings not shown. Gear 7 is driven by a gear 8 and driving shaft 9. The head carries arms 10 upon which are supported electric furnaces 11 through bails 12. When stationary the furnaces hang in the positions shown in full lines in Figure l but when the'head is revolved the furnaces extend progressively with increase in speed of rotation to the position shown in dotted lines in this figure.

The furnaces shown are equally balanced and are of the same type adapted to counter-balance each other during operation.

In the illustration the furnace 11 is of the coreless inductor type. It receivescurrent through rings 13 and 14, brushes l5 and 16 and conductors l7, l8, l7 and 18' by which the inductors 19 and 19' are fed. Crucibles 20 and 20' are shown in Figure l and 20 in Figure 1a. The molten charge is shown at 21in each furnace in Figure 1. .The brushes are supported upon brackets 22.

The connections between the brushes are flexible and provide continued connectionbetween the furnaces and the source of energy to the collector rings, here shown diagrammatically at 23 and 24.

Where any considerable length of time of settling of the molten content is required it is high lydesirable and generally necessary that the electrical connection with the furnace be maintained during the centrifuging operation as the molten too content would otherwise unduly cool and. the centrifuging would cease to be effective as the cooling charge became less freely fluid. Where the operation of centrifuging requires but a brief time, too short for cooling to be objectionable it 105 is not necessary that the furnace be operated as a furnace during the centrifuging and connections for supplying current to the furnace while nace walls, as in the case of an electrically nonconducting content such as glass, or by heating an electrically conducting content 21' by applying an induced current through the molten content as is intended in Figure la, where the crucible is non-conducting.

It will be evident that my invention ismuch moresatisfactory in elimination of gases or vapors and in consolidation of the molten content than a pressure upon the surface of the content would be, yet does not disturb the mass of the molten content. By my method each element of the content independently as well as in conjunc- 'tion with the other elements exerts a pressure upon the molten content between it andthe bottom of the pool, whereas with a pressure on the surface this independent action is. not present.

It will be evident that any number of furnaces may be centrifuged at the same time provided they be so placed as to balance their centrifugal effects. Two only are shown in the illustrations intended to be of substantially equal centrifugal effect and located on opposite sides of the axis of rotation.

It will be evident that the main advantage from my invention of securing the centrifuging pressure upon the content while maintaining the position of this content in the furnace'pool may be secured with any form of furnace for example, a nichrome resistance furnace, and the form of furnace is of value chiefly for its adaptability to the needs of treatment of the charge or to the convenient, effective and economical application of heat to the charge.

From this standpoint in the treatment of glass or quartz the crucible of my furnace may be made up from a bottom and rings forming the sides, permissibly using an alloy of tungsten carbide and nickel. This crucible may be heated by induction from current passing through a coreless inductor advantageously. This form of furnace is disclosed at length in an application by me intended to be copending herewith.

Where it is desired to have the charge as quiescent as possible for the purpose of removing air or gas. from the content, as in the centrifuging of glass, for example, the furnace crucible should be electrically conducting, whether the charge be electrically conducting or not. The frequency should be high enough so that the current induced will not extend to a radial depth greater than that of the crucible, to improve the power factor where the charge is now conducting and to prevent stirring of the quiescent pool where the pool is conducting.

However, the induction of electric current within the charge may be used to advantage where it is desired to stir the molten content, and this stirring can be made slight or considerable according to the desire of the designer.

The lower the frequency the higher will be the stirring effect as compared with the heating effect. For particular uses, therefore, the frequency may be selected with a view of securing a proper ratio between heating effect and stirring effect. The stirring is further within the control of the designer because the stirring belt can be selected by selection of the belt (vertically) occupied by the primary inductor coil. For example, a low belt such as that shown in Figure 1a will stir the lower part of an electrically conducting content without the stirring being nearly so effective near the surface of the pool. A stirring belt at the middle or covering the entire height of the pool as in Figure 1 will place.

stir an entire electrically conducting mass, whereas a belt located about the upper part of the charge will stir the upper part chiefly.

Where melting takes place in the centrifuge furnace, as will almost always be desirable the electric current should .be reduced during centrifuging so as to add heat enough merely to maintain the desired temperature. I have not considered it necessary to show means for this purpose as the current can be controlled by many different means outside of the furnace.

In operation, thecharge is placed within the furnace in solid or molten condition as preferred and is melted or heatedin the furnace to the temperature at which centrifuging is to take If the heat upon the charge is to be maintained, as is much the more desirable and as is essential where centrifuging is to be continued for a considerable time, the initial temperature need not be as high as would be required where the heat is to be cut off from the furnace during centrifuging. In this latter case, permissible for brief centrifuging only, it is desirable to superheat the content somewhat before beginning centrifuging.

In view of my invention and disclosure variations and modifications to meet individual whim or particular need will doubtless become evident to others skilled in the art to obtain all or part of the benefits of my invention without copying the structure shown, and I, therefore, claim all such in so far as they fall within the reasonable spirit and scope of my invention.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

l. The method of eliminating bubbles quickly from glass or quartz which consists in melting the glass or quartz and in swinging the molten body of glass or quartz bodily about an axis outside .of it while maintaining the centrifugal pressure thus produced in a direction perpendicular to the normal surface of the body, whereby the apparent density is increased and the bubbles are forced to the surface of the body of the glass or quartz.

2. The method of eliminating bubbles quickly from glass or quartz which consists in melting a charge of glass and in centrifuging the molten glass while the bubbles are allowed to come to the normal surface and the centrifugal pressure is maintained perpendicular to the bottom of the container.

3. The method of treating an electrically conducting charge which consists in melting it, in maintaining it melted by inducting electric current in it at a point chiefly below the center of the height of the charge and in centrifuging it about an axis outside of itself while maintaining the heating induction within the lower part of the charge thus increasing the apparent density to bring the bubbles to the surface.

4. The method of treating a molten electrically conducting charge, which consists in centrifuging it about an axis outside of the charge and at the same time adding to its heat and stirring it by induction of electric current chiefly within the lower part of the body of the charge.

5. An electric induction furnace having a coreless inductor and electrically conducting crucible naces, mounts for the furnaces adapting them to 5 swing outwardly in balanced relation with respect to the axis, electrical connections for the furnaces adapted to be maintained in all positions of the furnaces and means for revolving the furnaces rapidly while maintaining electrical connection v therewith to centrifuge the furnace contents.

'7; In mechanism for heating and treating a molten charge, an electric furnace having an electrically non-conducting holder for the charge, an electric inductor about the lower part of the charge, means for applying current to the in- EDWIN F. NORTHRUP. 

